What I got from that is "fast and intuitive" is the must have. When you have a choice (backend bit), justify you decision. I'd try to use that to stand out or an additional cool feature. When I have to do such homework, I do the requirements to what I think an above average candidate would, they've seen this a million times, then add 1-2 bits of flair/coolness only a handful of people would do to pique their curiosity and want to ask about the next round